|ATP Finals 2020|
|Venue: O2 Arena, London Date: 15-22 November|
|Coverage: Watch live on BBC Two, BBC iPlayer, BBC Sport website and mobile app; follow BBC radio and live text commentary online on selected matches|
Top seed Novak Djokovic started his bid for a record-equalling sixth ATP Finals title with a classy win over Argentine debutant Diego Schwartzman.
The 33-year-old Serb, who has not won the event since 2015, eased to a 6-3 6-2 victory at the O2 Arena in London.
In Monday's evening session, Russian fourth seed Daniil Medvedev earned his first ATP Finals match win by beating German fifth seed Alexander Zverev.
Medvedev lost all his group matches in 2019, but began with a 6-3 6-4 win.
The season-ending event is being played behind closed doors because of the coronavirus pandemic.
That has led to a flat and eerie atmosphere at the near 18,000-seat arena, meaning London has been unable to wave farewell to the event - which moves to Turin in Italy next year - like tournament organisers would have intended.
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Nevertheless, the lack of atmosphere did little to disrupt Djokovic in what proved to be a high-quality performance.
Perhaps there was a touch of nerves from the 17-time Grand Slam champion as he lost serve in the third game of the opening set, but he quickly settled to break straight back and then tighten his grip on the match.
Now hitting metronomically and moving freely, Djokovic wore down Schwartzman's service game again for a 5-3 lead and held his own serve to take the opening set.
On not being able to consolidate the break, Schwartzman said: "It is difficult when you have just a small chance against Djokovic and you don't make that chance. I did wrong things and from then it is a difficult match."
Schwartzman, 28, has enjoyed a fine season in a disrupted 2020, reaching his first Grand Slam semi-final at the French Open in October and cracking the world's top 10 for the first time.
While his game is built on reliable hitting from the baseline and athleticism, it was not enough for the 5ft 7in Argentine to find a way past Djokovic.
Schwartzman knew he had to take some risks to break down Djokovic, but that translated into 10 unforced errors and just four winners in the opening set.
Sustaining his level and forcing Schwartzman into more mistakes was made to look easy by Djokovic in the second set as the Serb broke twice for a 4-1 lead and went on to clinch a straightforward win in one hour and 18 minutes.
"The second set I started swinging through the ball more and with less hesitation," Djokovic said. "I was very pleased with the way I played."
Medvedev picks up where he left off in Paris
After a chastening experience on his Finals debut last year, Medvedev is hoping to acquit himself better on his second appearance and made the perfect start by matching Djokovic's straight-set win in Group Tokyo 1970.
In truth, it was a gruelling and scrappy battle between the two players who contested last week's Paris Masters final, with Medvedev outlasting the German to back up his victory in the French capital.
"Confidence is key for sure, not only the final against him but winning a Masters always helps," said 24-year-old Medvedev, who faces Djokovic on Wednesday.
"It was a little bit shaky at the start, but we had some unbelievable points and the intensity was one of the most I've had in my career."
The opening six games took more than 40 minutes and contained 58 points, but it was Medvedev who tipped the first set in his favour - thanks in part to Zverev's old failing of a weak second serve hampering him again.
The 23-year-old German, who won the 2018 Finals, broke in the very first game of the match, only to lose his own serve from 30-0 in the second after missing seven successive serves.
Two more double faults from Zverev in that sixth game proved pivotal and, as the match opened up in the second set after that high octane start, Medvedev broke again for a 4-3 lead.
He held on to that advantage, even delivering an underarm serve that helped him win the point at 30-30 in the next game.
"All in all, it wasn't a good match for me. I think since the restart of the season, it was one of the worst ones," said Zverev, who reached the US Open final in September.
In the doubles, there were opening wins for top seeds Bruno Soares and Mate Pavic, and fourth seeds Marcel Granollers and Horacio Zeballos.
What's happening on Tuesday?
Spanish second seed Rafael Nadal meets Austrian third seed Dominic Thiem in Group London 2020 - a match you can watch on BBC Two and the BBC Sport website and app from 14:00 GMT.
Both players won their opening matches on Sunday, meaning Russian debutant Andrey Rublev and Greece's defending champion Stefanos Tsitsipas search for their first wins when they play in the evening session (20:00 GMT).
Britain's Joe Salisbury and his doubles partner Rajeev Ram look to back up their winning start with another victory when they face Croatia's Nikola Mektic and Wesley Koolhof of the Netherlands at 18:00 GMT.
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